1. Field of the Invention
This invention relates to an improved cooking and heating receptacle for food in which the flow of heat from the resistor or electrical heating conductors to the food is controlled by a thin flexible polymeric heating element or laminate. The thermal charasteristics of the laminate controls the rate of heat transferred from the resistor into the food elminating hot spots along the path of the resistors (normally encountered in conventional heating elements) and thereby retaining the temperature levels of the food below its scorching temperature without the necessity of metallic or liquid heat diffusers, mixing the food during heating, etc.
2. Description of the Prior Art
Considerable prior art has been directed to various means for evenly distributing or transferring heat in cooking vessels from the heat source into the food. Many prior artisans have used metal as the means for diffusing the heat.
For example, U.S. Patent No. 2,603,740 issued July 15, 1952 to E. Del Buttero shows a thick walled heating pan with an integral resistor. The thick metal walls of the pan serve as the means for diffusing heat. However, thick metal walls are not sufficient to evenly distribute the heat. Food in heating pans of this nature needs constant attention such as mixing or stirring to prevent the food from scorching or burning. This is a basic problem with most all prior art devices as there is a lack of proper heat distribution at the interface of the pan and food.
U.S. Pat. No. 3,875,370 issued Apr. 1, 1975 to L. G. Williams, shows a bar or aluminum 11 encased in a resin jacket and disposed below the surface of the cooking dish for the purpose of serving as a heat distributor. A heating element 29 may be embedded in the aluminum distributor.
U.S. Pat. No. 3,010,006 issued Nov. 21, 1961 to F. C. Schwaneke, shows a metallic heating receptacle with a metal heat distributing member 28 interfaced directly with the heating pan or receptacle 10.
U.S. Pat. No. 3,798,415 issued Mar. 19, 1974 to E. M. Graham, discloses an aluminum diffuser 6 of varying thickness for the purpose of diffusing or distributing heat along the bottom of a thin walled pan. Other teachings such as that disclosed in U.S. Pat. No. 2,969,452 issued Jan. 24, 1961 to T. L. Geller et al use a liquid such as silicone oil which may be placed in a chamber 16 adjacent to or under the cooking receptacle per se. See particularly FIG. 3 of Geller.
Other artisans have directed their attention to embedding heating elements in laminated structures. For example, U.S. Pat. No. 2,804,533 issued Aug. 27, 1957 to M. Nathanson discloses a heating element embedded in a polymeric lamina. The heating element can be adapted to devices such as space heaters or heaters for heating solids or liquids. It contains a conducting wire 5 held to mat 2 which in turn is encased in insulating mats 3 and 4.
U.S. Pat. No. 2,938,990 issued May 31, 1960 to H. Levine, shows a calrod type of heating element 6 encased in insulating material which in turn is placed in a metallic sheath 8 brazed to the wall of the cooking receptacle.
U.S. Pat. No. 3,597,591 issued Aug. 3, 1971 to David L. Van Derlip shows an electrical conductor 14 of fiberglass and aluminum particles sandwiched or encased between Teflon insulation layers 12 and 13. See FIG. 4.
Another integral laminated heating element is disclosed in U.S. Pat.No. 3,909,591 issued Sept. 30, 1975 to John B. Ulam. This patent illustrates an arcuate heating element 40 laminated to the bottom of the heating receptacle.
U.S. Pat. No. 3,191,004 issued June 22, 1965 to J. P. Hocker also shows a laminated heating element. In this reference an RTV adhesive is vulcanized to the heating receptacle with the heating element per se laminated between silicone rubber sheets 28 and 30.
Other artisans have used thin polymeric heating elements in connection with cookware but have controlled the distribution of heat by utilizing heating elements with different power intensities. For example, see U.S. Pat. No. 3,869,596 issued Mar. 4, 1975 to John R. Howie wherein the heating element illustrated in FIG. 4 is divided into three general areas each with different power densities to provide for the requisite amount of heat to be transferred to different areas of the cooking vessel and the food therein.
A good deal of prior art has been directed to utilizing thermostats to control the outer parameters of heat to be generated and transferred from the heating receptacle into the food. An exemplary patent is U.S. Pat. No. 2,480,337 issued Aug. 30, 1949 to G. C. Pearce which shows a bimetallic thermostat 52 connected directly to the bottom of the receptacle which contains the food to be heated.
Additionally, thermostats have been used to control the initial generation of heat and once a predetermined level of heat is attained, retain such level by "hold-heating", i.e. by de-energizing a portion of the resistor. For example, U.S. Pat. No. 1,678,885 issued July 31, 1928 to I. G. Thomas shows a heating device with a series of heating elements 17-21. All of the elements are energized to initially heat the material to predetermined levels and then thermostat 24 is opened to cut out part of the resistors leaving resistors 18 and 19 energized for continuous or "hold-heating" at a lower level.
U.S. Pat. No. 3,725,645 issued Apr. 3, 1973 to Thomas S. Shevlin, shows a cooking dish similar to that disclosed in the instant invention. However, Shevlin teaches the introduction of heat in pulses so that the heat (ranging from 211 to 223 B.T.U. in 10-20 minutes) introduced into the food is absorbed during intermittent periods when energy is not applied to the heating element. For this reason the surface of the low heat capacity dish supporting the food does not transfer heat to the food at temperature levels that would scorch the food.